1. Field of the Invention
The present invention relates to a system for the inspection of the inside surfaces of objects for defects and, more particularly, for the inside surface inspection of containers such as aluminum beverage cans for a variety of surface imperfections and defects.
2. Statement of the Problem
A need exists in manufacturing environments for high speed inspection of the inside surfaces of objects such as aluminum beverage cans. Conventional manufacturing processes move such aluminum beverage cans along a conveyor at line speeds of 1200 to over 2000 cans per minute. During the manufacturing process for the aluminum beverage cans, a number of inside surface conditions can be created which would cause the can to be rejected. The inside surfaces of the cans, for example, should be round and free of physical defects such as dents and the like and the inside surfaces should be free of grease, oil, blistering, or debris. In addition, the flange should be free of knockdowns.
Complicating the problem of inside surface inspection is the geometry of the beverage can. A typical beverage can such as that shown in FIG. 1, has a number of curved surfaces which make surface inspection difficult especially when illuminated light is delivered into the can and the reflection off such curved surfaces makes it difficult to inspect nearby or adjoining surfaces.
Hence, a need exists for a high speed inside surface inspection system which does not interfere with the operation of a normal conveyor line carrying beverage cans and which is capable of inspecting the surfaces for small sized defects such as, for example, 0.040 inches in a fashion that does not interfere or obstruct the manufacturing process of the cans.
3. Solution to the Problem
The present invention provides a solution to the above problem, in one embodiment, by providing a series of three physically spaced cameras along a conventional conveyor line. Depending upon the inside surface of the object being inspected, two or more cameras can be utilized. In addition, one camera could be utilized to inspect a selected area inside the object such as the moat of an aluminum beverage can. Each camera captures an image of the inside of the beverage can at a different horizontal location in the can. Undesirable and interfering reflections of light from the illumination of the interior of the can are selectively masked out so that the captured image of the area next to the severe reflection can be thoroughly analyzed.
The system of the present invention is capable of inspecting for defects and imperfections down to about 0.040 inches in size, but the invention is not limited to this resolution. The system of the present invention does not interfere with the travel of the cans along the conveyor line unless a defect is sensed in a given can which is then rejected from the line.